1. Field of the Invention
This invention relates to settable epoxy resin composition that has been rendered flexible by incorporating a novel liquid chloroprene copolymer therein.
2. Description of the Prior Art
Because of their good characteristics, epoxy resins are conventionally used in casrtings, impregnating agents, adhesives, sealants, paints, etc. However, since their cured product essentially has low flexibility, there has been a pressing need to improve the impact strength thereof and the ability to bond flexible materials therewith.
Two conventional types of agents can be used to render epoxy resins flexible: one agent is a non-reactive type agent such as a phthalic ester and chlorinated diphenyl, and the other agent is a reactive type agent such as a long-chain monoepoxy compound, a polyester having a terminal hydroxyl group, a polyamide resin, a liquid polysulfide polymer having a terminal mercapto group and liquid acrylonitrile-butadiene rubber (NBR) having a terminal carboxyl group. Reactive type agents are generally advantageous because they can render settable epoxy resins flexible without causing a significant deterioration in the properties of the resin to occur, and in particular, a polyamide resin, a liquid polysulfide polymer having a terminal mercapto group and liquid NBR having a terminal carboxyl group are widely used. However, a settable epoxy resin which has been rendered flexible by a polyamide resin is not sufficiently resilient to absorb an instantaneous impact or an impact at low temperature. If an eposy resin is rendered flexible using a liquid polysulfide polymer, the resin sets so fast in the presence of an amine compound, which is a typical curing agent for epoxy resins, that it becomes difficult to control the pot life of the epoxy resin and the cured resin does not have sufficient toughness. A flexible epoxy resin containing liquid NBR is less reactive at low temperatures, and so, if curing is at room temperature only a product with poor characteristics can be obtained.